In patients with aortic stenosis routine preoperative hemodynamic assessment does not accurately predict long-term post-operative prognosis. Such assessments are performed with the patient at rest. Therefore, we used radionuclide cineangiography during exercise to assess left ventricular functional reserve capacity to determine accurately the functional status of the left ventricle, the relationship of ventricular function during exercise to prognosis and the effects of aortic valve replacement on left ventricular function. We found that, while left ventricular function commonly is depressed during exercise before operation, function almost invariably returns to normal during exercise after operation, irrespective of the severity of the previously present valvular stenosis.